Pressurized refiner seal assembly

ABSTRACT

A seal assembly for sealing the passage of a rapidly rotating axially adjustable shaft through a pressurized housing containing particulate materials such as pulp fibers. The shaft is journaled within an axially adjustable quill disposed exteriorly of the housing. A quill extension surrounding the shaft is sealed for axial movement with respect to the housing by a packing gland. The rotating shaft is sealed with respect to the quill extension by a labyrinth seal and a mechanical seal having a pressurized liquid cooling system. Means are provided to permit a purging flow of the pressurized liquid into the labyrinth to prevent particulate material from reaching the mechanical seal, the pressurized cooling system liquid being at a higher pressure than the interior of the housing.

United States Patent [4 Oct. 31, 1972 Fisher [54] PRESSURIZED REFINER SEAL ASSEMBLY [72] Inventor: Chester Donald Fisher, Muncy, Pa. [73] Assignee: Sprout, Waldron 8: Company, Inc., Muncy, Pa. 7 [22] Filed: July 22, 1971 [21] Appl. No.: 165,211

[52] US. Cl ..241/256 [51] Int. Cl ..B02c 7/11 [58] Field of Search ..241/245, 255, 256

[56] References Cited UNITED STATES PATENTS 3,038,673 6/1962 Fisher ..241/256 X 3,224,689 12/1965 Behrens et a]. ..241/256 3,276,701 10/1966 Fisher ..241/256 X Primary Examiner-Granville Y. Custer, Jr. Attorney-Charles l-l. Howson, Jr. et a].

[5 7] ABSTRACT A seal assembly for sealing the passage of a rapidly rotating axially adjustable shaft through a pressurized housing containing particulate materials such as pulp fibers. The shaft is journaled within an axially adjustable quill disposed exteriorly of the housing. A quill extension surrounding the shaft is sealed for axial movement with respect to the housing by a packing gland. The rotating shaft is sealed with respect to the quill extension by a labyrinth seal and a mechanical seal having a pressurized liquid cooling system. Means are provided to permit a purging flow of the pressurized liquid into the labyrinth to prevent particulate material from reaching the mechanical seal, the pressurized cooling system liquid being at a higher pressurev than the interior of the housing.

13 Claims, 4 Drawing Figures minimums-1 m2 370L488 SHEET 1. BF 2 INVENTOR? CHESTER DONALD FISHER AT TYS FEW um i am SHEEI 0F 2 PRESSURIZED REFINER SEAL ASSEMBLY The present invention relates generally to seal assemblies for sealing the passage'of a rotating, axially adjustable shaft through the wall of a pressurized housing. More particularly, the invention relates to a novel seal assembly as described adapted for sealing the drive shaft of a high capacity steam pressurized refiner for refining wood chips and similar materials.

In the processing of wood chips for hardboard manufacturing, it has been found that the refining of the chips can be carried out with a considerable saving in power if the chips are refined under steam pressure. One type of refiner used for this purpose is of the socalled disc type which is characterized by a pair of opposed parallel discs adapted for relative rotation, each disc carrying a refining plate having attrition elements on its working face. The discs may each be rotated in opposite directions, or one disc may be fixed with the other rotated. The material to be refined is usually introduced between the plates at their center, and is advanced across the closely spaced attrition elements by centrifugal force.

In order to adjust the spacing between the disc plates to control the refining action, it is necessary that the drive shaft on which one of the discs is mounted be axially adjustable. Since the shaft is journaled and driven exteriorly of the pressurized housing, some type of shaft seal is required where the shaft passes through the housing which will accommodate boththe rotary motion of the shaft as well as its axial movement during adjustment of the plate spacing.

For the relatively small low-speed refiners which have until recently been used for pressurized service, a conventional packing gland has been satisfactory to seal the shaft against the housing pressure. These machines might typically operate within the speed range of 600 to 900 rpm, and due to their low horsepower utilized a relatively small shaft, thus producing a low linear speed of the shaft surface where the seal is applied.

Modern disc refiners, however, are typically built to rotate at speeds of 1,500 to 1,800 rpm with power applied to the drive shaft on the order of 1,000 to 2,500 horsepower. Such power input requires a shaft of substantial diameter, and this factor coupled with the relatively high speed of rotation produces a linear speed at the shaft surface that is too great for sealing by means of a packing gland. The high surface speed develops a high amount of frictional heat which would quickly wear out conventional packing. Although a mechanical seal could accommodate the high surface speed of the shaft, it could not accommodate the axial shaft movement required to adjust the plate spacing.

In the present invention, a seal member is provided overlying the shaft at its passage through the housing, which member is adapted to move axially with the shaft. A conventional packing gland is employed to seal the seal member with respect to the housing, while a labyrinth seal in combination with a mechanical seal are employed between the seal member and the shaft. A pressurized water cooling system for the mechanical seal is provided with a bleed passage opening into the region between the labyrinth seal and the mechanical seal to provide a purging flow of water through the labyrinth seal, the cooling system pressure exceeding the steam pressure within the refiner housing. In a preferred embodiment of the .invention wherein the shaft is journaled within a quill axially movable therewith, the seal member comprises an extension of the quill.

It is accordingly a first object of the present invention to provide a novel seal assembly for sealing the passage of a rotating axially adjustable shaft through the wall of a pressurized housing.

A further object of the invention is to provide a seal assembly as described adapted for sealing the drive shaft of a steam pressurized refiner operating at high shaft surface speed.

Additional objects and advantages of the invention will be more readily apparent from the following detailed description of a specific embodiment thereof when taken together with the accompanying drawings wherein:

FIG, 1 is a vertical axial sectional view of a pressurized refiner incorporating a seal assembly in accordance with the present invention;

FIG. 2 is a greatly enlarged view of the area indicated in FIG. 1 showing the details of the present seal assembly;

FIG. 3 is a partial sectional view of a portion of the mechanical seal of the seal assembly of FIGS. 1 and 2; and

FIG. 4 is a view similar to FIG. 3 showing an additional partial sectional view of the mechanical seal.

Referring to the drawings, and particularly FIG. 1 thereof, a pressurized refiner generally designated 10 as shown and includes a base 12 supporting a pressurized housing 14. Within the refining chamber 16 defined by the housing 14 are disposed a pair of parallel spaced discs 18 and 20 to the confronting faces of which are secured the respective refining plates 22 and 24. The plates, which conventionally comprise precisely machined and balanced sets of plate segments, are characterized by attrition elements such as ribs or teeth on their working faces.

The disc 18 is secured by bolts 26 to the housing 14 and is thus fixed in position within the refining chamber 16. The disc 20 is mounted on one end of the drive shaft 28 for rotation therewith. To vary the spacing between the plates 22 and 24 and hence the refining action of the plates, the shaft 28 is axially adjusted as will be presently described. Material to be refined is introduced axially between the refining plates through the axial inlet passage 30 and is discharged from the refining chamber through the radial discharge port 32.

The shaft 28 is journaled by roller bearing 34, ball bearing 36 and thrust bearing 38 within a quill 40 which is slidably disposed on quill support members 42 and 44 of the base. Rotation of the quill is prevented by keys 46 cooperating with keyways 48 in the quill, the keys being spring loaded by springs 50 disposed within the spring retainer assemblies 52 attached to the quill support members.

The quill 40 and hence the shaft 28 and attached disc 20 and plate 24 are axially positioned by means of a positioning device 54 mounted on yoke 56 on the base 12. In the present instance, the positioning device comprises a motor driven worm acting on the threaded positioning stud 58 secured to the arm 60 attached to the outer end of the quill 40. The keyways 48 are elongated to permit a predetermined range of axial movement of the quill and shaft. The shaft extends beyond the quill and the base and is provided with a sheave 62 which is keyed thereto for coupling the shaft to a suitable power source such as an electric motor. The above described refiner structure is essentially conventional and the present invention is directed to the novel seal assembly generally designated 64 for sealing the passage of the shaft 28 through the wall of the pressurized housing 14. Referring to FIG. 2 wherein one-half of the axially symmetrical seal assembly is shown in detail, the assembly considered broadly includes a quill extension 66 extending axially from the quill intermediate the housing and the shaft, a packing gland assembly 68 sealing the quill extension 66 with respect to the housing 14, a labyrinth seal 70 between the quill extension 66 and the shaft 28, and a mechanical seal 72 adjacent the labyrinth seal between the quill extension and the shaft 28.

Considering first the quill extension 66, it will be noted that the inner end of the quill 40 terminates in radially spaced relation to the cylindrical passage 74 in the housing 14 through which the shaft passes. The quill extension includes a seal member 75 having a cylindrical outer surface 76 and a cylindrical neck portion 78 which is seated and sealed by suitable O-ring seals against a cooperatively shaped and dimensioned seat 80 of the quill end. The quill extension further includes a purge ring 82 having a cylindrical outer surface 84 of the same diameter as the surface 76 of the seal member 75 and being coaxially aligned therewith by means of a sealed shouldered joint as illustrated. Bolts 86 extending axially through the purge ring 82 and seal member 75 are threaded into the end of the quill to secure the elements of the quill extension to the quill for axial movement therewith and hence with the shaft.

The packing gland assembly 68 comprises a ring shaped gland element 88 fixedly secured to the housing 14 within the passage 74. The element 88 is provided with an annular slot 90 within which packing 92 is disposed for cooperation with the surface 76 of the quill extension seal element 75. A packing gland follower 94 is secured to the element 88 by bolts 96 which are tightened to compress and seal the packing 92 in a well known manner.

The labyrinth seal 70 and the mechanical seal 72 are formed between the quill extension and the shaft by various elements including a collar 98 locked to the shaft and sleeves 100 and 102 which are pinned to each other and the collar 98 for rotation with the shaft. The labyrinth seal 70 includes inwardly radially directed tooth-shaped elements 104 of the purge ring which extend closely adjacent the cylindrical outer surface of the collar 98. The labyrinth seal further includes a lip seal element 106 cooperatively positioned adjacent the outer cylindrical surface of the sleeve 100. The lip seal 106 is pinned to the seal member 75 of the quill extension.

Supplementing the labyrinth seal between the quill extension and shaft is an additional labyrinth defined by axially extending tooth-shaped elements 108 of the purge ring 82 which cooperate with the rear surface 110 of the disc 20 to prevent material from reaching the region of the collar 98. A steam purge line 112 opening into the region between the elements 108 and the disc rear face permits a bleed of steam under pressure into this region to further prevent the passage of material into the shaft seal. The purge line 112 in the purge ring 82 is fed by the steam passage 114 in the gland element 88 into which steam is directed through the inlet port 1 16.

The mechanical seal 72 is basically of a conventional mechanical seal structure and includes fixed seal rings 1l8'and which are respectively pinned and sealed to the quill extension and quill end and define seal surfaces 122 and 124 respectively. Rotating seal elements 125 and 126 having respective seal faces 128 and 130 respectively oppose the elements 118 and 120 with the seal faces thereof in sliding engagement. The seal elements 125 and 126 are respectively pinned to the compression rings 132 and 134 respectively for rotation therewith. The rings 132 and 134 are as shown in FIG. 4 axially urged apart by a plurality of springs 136 spaced therebetween which pass through a ring 138 mounted on sleeve 102 for rotation therewith and with the shaft, the screws 140 in the ring 138 extending into spaced radial holes 142 in the sleeves. Altemately spaced circumferentially around the assembly between the springs 136 are a plurality of pins 144 extending from the compression rings 132 and 134 and slidable within axial bores 146 in the ring 138 to insure rotation of the rings 132 and 134 and hence the seal members 125 and 126 with the shaft. O-rings 147 and 148 respectively positioned between the seal elements 125 and 126 and their corresponding compression rings 132 and 134 seal the openings between the compression rings 132 and 134 from fluid penetration and also uniformly convey the axial force of the compression springs 136 to the cooperating seal elements 125 and 126.

A cooling system is provided for cooling and lubricating the mechanical seal and comprises a water inlet port 150 in the quill opening into passage 152 in the quill aligned with a corresponding passage 154 in the seal member 75 which opens into an annular chamber 156 adjacent the mechanical seal. Cooling water under pressure admitted into the chamber 156 is discharged through discharge passage 158 in element 75 and the aligned passage 160 in the quill and into a suitable conduit attached to discharge port 162.

An important aspect of the seal assembly is the means provided for bleeding a flow of the pressurized liquid coolant for the mechanical seal into the labyrinth seal to provide a purging flow against the intrusion of particulate matter. In the preferred embodiment, this means comprises at least one passage 164 in the seal element 118 which permits pressurized water to bleed into the region between the sleeve 100 and the mechanical seal to apply a higher pressure to this region than that in the refiner housing. There will consequentlybe a small but continuous flow of purging liquid from the mechanical seal toward and through the labyrinth seal vto sweep any wayward particulate material back into the pressurized housing. For this purpose, the cooling liquid should be at a substantially higher pressure than the refiner housing pressure for example 10-25 psi higher.

For operation of the refiner, the shaft 28 is rotated by a suitable drive means such as an electric motor connected with the sheave 62 to rotate the disc 20 and hence the refining plate 24 with respect to the fixed disc 18 and refining plate 22. Material to be refined is introduced through the inlet passage 30 into the center of the refining plates for passage between the plate surfaces. The refining chamber 16 is steam pressurized during the refining operation and the refined products are discharged through the discharge port 32. i v

To adjust the spacing of the refining plates, the positioning device 54 is actuated to axially adjust the quill 40 and the shaft, disc and plate 24 carried thereby. Although such axial adjustment is infrequently required, it may be made during the operation of the refiner to control the work done on the material passing between the plates.

During operation of the refiner, the seal assembly 64 functions to prevent the escape of pressurized steam and materials being refined into the atmosphere along the rotating andcaxially adjustable shaft. A flow of cooling water under a pressure substantially higher than the pressure within the refining chamber is introduced into the inlet port 150 for circulation within the chamber 156 surrounding the mechanical seal. The cooling water is discharged through discharge port 162 and upon cooling may be recirculated. The port 116 is connected with a conduit leading to a supply of steam under a somewhat higher pressure than the steam in the refining chamber to permit a purging flow of steam through the purge ring 82 adjacent the tooth-shaped elements 108 thereof to provide a flow of steam into the refining chamber along the rear surface 110 of the disc 20 to prevent particulate material from ap preaching the shaft seal region.

The operation of the various seal assembly elements has been described in connection with the description of the elements and need only briefly be reviewed. The packing 92 of the packing gland assembly 68 is adequate to seal the axially movable non-rotating quill extension with respect to the housing. The packing gland assembly 68 is of conventional design and in view of the fact that the axial adjustment is made infrequently and involves only a slight axial movement, any type of conventional packing arrangement or other sealing arrangement such as O-ring seals would be adequate to accomplish this scaling function.

The sealing of the shaft with respect to the quill extension is carried out by the mechanical seal which is provided with a cooling and lubricating liquid circulation system. The mechanical seal is protected from fouling by particulate material by means of the bleed of the cooling liquid, which is at a pressure greater than the refining chamber pressure, into the housing ahead of the mechanical seal. The labyrinth seal is preferably provided between the housing chamber and mechanical seal to permit a small but effective cooling liquid bleed fiow through the labyrinth to purge the labyrinth passages.

As indicated, the particular details of the mechanical seal are a matter of choice and the mechanical seal per se may be of a conventional construction. It has, however, beenfound that a mechanicalseal installed in a refiner of the type described without the provision of the cooling liquid bleed will be ineffective to provide the necessary sealing function due to the inevitable penetration of wood fibers between the seal faces. The cooperating seal surfaces 122 and 128 and 124 and 130 are precision machined surfaces and provide an efiective liquid and gas seal even at relatively high speed rotation of the shaft. However, solid material must be kept fromthe surfaces to maintain the integrity of the seal and this is the function of the cooling liquid bleed ahead of the mechanical seal.

Although the present invention is shown in the setting of a refiner wherein only one of the opposed discs is rotated, it will be obvious that the seal assembly is equally well suited for use in a refiner wherein both discs are rotated in opposite directions. The seal assembly furthermore has broad applications to any device wherein a rotating, axially adjustable shaft is to be sealed at its passage through a pressurized housing.

Manifestly, changes in details of construction can be effected by those skilled in the art without departing from the spirit and the scope of the invention.

Iclaim:

l. A sea] assembly for sealing the passage of a rotating axially adjustable shaft through a pressurized housing, said assembly including means between said shaft and said housing overlying said shaft and adapted for axial movement therewith, means for sealing said first means with respect to said housing, a mechanical seal mounted between said first means and said shaft and adapted to move axially with said first means and shaft, a pressurized liquid cooling system; for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.

2. A seal assembly for sealing the passage of a rotating axially adjustable shaft through a pressurized housing containing particulate material, said shaft being joumaled within a quill disposed exteriorly of the housing and adapted for, axial movement with respect thereto, said assembly comprising a quill extension extending from said quill between said shaft and said housing adapted for axial movement with said shaft, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.

3. The invention as claimed in claim 2 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal to provide a flow of liquid through said labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.

.4. The invention as claimed in claim 2, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating one of said seal elements being connected to said shaft for rotation therewith, and means for resiliently biasing said seal elements together to provide a sealing engagement of said sealing surfaces.

5. In a refiner comprising a housing adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed surfaces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, an axially adjustable drive shaft extending through said housing and including means for supporting and driving one of said plates in rotation, means for rotating said drive shaft, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, and means for pressurizing said housing during the refining operation, the improvement comprising a seal assembly for sealing the passage of said shaft through said housing, said seal assembly comprising a seal member overlying said shaft intermediate said shaft and said housing and adapted for axial movement with said shaft, means for sealing said seal member with respect to said housing, a mechanical seal mounted between said seal member and said shaft and adapted to move axially with said seal member and said shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.

6. in a refiner comprising a housing adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed surfaces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, and axially adjustable drive shaft extending through said housing and including means for supporting and driving one of said plates in rotation, means for rotating said drive shaft, said shaft being joumaled within a quill disposed exteriorly of said housing and adapted for axial movement with respect thereto, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, and means for pressurizing said housing during the refining operation, the improvement comprising a seal assembly for sealing the passage of said shaft through said housing, said seal assembly comprising a quill extension extending from said quill between said shaft and said housing adapted for axial movement with said shaft, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.

7. The invention as claimed in claim 6 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal-to provide a flow of liquid through said labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.

8. The invention as claimed in claim 6, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating one of said seal elements being connected to said shaft for rotation therewith, the means for resiliently biasing said seal elements together to provide a sealing engagement of said sealing surfaces.

9. A pressurized refiner for refining wood chips and like materials, said refiner comprising a base, a housing on said base adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed refining faces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, an axially adjustable drive shaft passing through said housing, one of said plates being mounted on said drive shaft for rotation therewith, the other of said plates being fixed to said housing, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, means for pressurizing said housing with steam during the refining operation, said shaft being joumaled within a quill disposed exteriorly of said housing, means on said base for supporting said quill to permit axial movement thereof with said shaft, means for rotating said shaft, means on said base providing selective axial positioning of said quill and said shaft and plate carried thereby, a seal assembly for sealing said shaft at its passage through said housing, said seal assembly comprising a quill extension extending axially from said quill and circumferentially-overlying said shaft intermediate said shaft and said housing, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.

10. The invention as claimed in claim 9 wherein said means for sealing said quill extension for sliding axial movement with respect to said housing comprises a packing gland assembly.

11. The invention as claimed in claim 9 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal to provide a purging flow of liquid through said labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.

12. The invention as claimed in claim 9, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed parallel sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating'one of said seal elements being connected to said shaft for rotation therewith, and means for resiliently biasing 

1. A seal assembly for sealing the passage of a rotating axially adjustable shaft through a pressurized housing, said assembly including means between said shaft and said housing overlying said shaft and adapted for axial movement therewith, means for sealing said first means with respect to said housing, a mechanical seal mounted between said first means and said shaft and adapted to move axially with said first means and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.
 2. A seal assembly for sealing the passage of a rotating axially adjustable shaft through a pressurized housing containing particulate material, said shaft being journaled within a quill disposed exteriorly of the housing and adapted for axial movement with respect thereto, said assembly comprising a quill eXtension extending from said quill between said shaft and said housing adapted for axial movement with said shaft, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.
 3. The invention as claimed in claim 2 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal to provide a flow of liquid through said labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.
 4. The invention as claimed in claim 2, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating one of said seal elements being connected to said shaft for rotation therewith, and means for resiliently biasing said seal elements together to provide a sealing engagement of said sealing surfaces.
 5. In a refiner comprising a housing adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed surfaces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, an axially adjustable drive shaft extending through said housing and including means for supporting and driving one of said plates in rotation, means for rotating said drive shaft, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, and means for pressurizing said housing during the refining operation, the improvement comprising a seal assembly for sealing the passage of said shaft through said housing, said seal assembly comprising a seal member overlying said shaft intermediate said shaft and said housing and adapted for axial movement with said shaft, means for sealing said seal member with respect to said housing, a mechanical seal mounted between said seal member and said shaft and adapted to move axially with said seal member and said shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.
 6. In a refiner comprising a housing adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed surfaces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, and axially adjustable drive shaft extending through said housing and including means for supporting and driving one of said plates in rotation, means for rotating said drive shaft, said shaft being journaled within a quill disposed exteriorly of said housing and adapted for axial movement with respect thereto, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, and means for pressurizing said housing during the refining operation, the improvement comprising a seal assembly for sealing the passage of said shaft through said housing, said seal assembly comprising a quill extensiOn extending from said quill between said shaft and said housing adapted for axial movement with said shaft, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.
 7. The invention as claimed in claim 6 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal to provide a flow of liquid through said labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.
 8. The invention as claimed in claim 6, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating one of said seal elements being connected to said shaft for rotation therewith, the means for resiliently biasing said seal elements together to provide a sealing engagement of said sealing surfaces.
 9. A pressurized refiner for refining wood chips and like materials, said refiner comprising a base, a housing on said base adapted for pressurization, a pair of juxtaposed refining plates having attrition elements on the opposed refining faces thereof, said plates being disposed in parallel closely spaced relation within said housing and adapted for relative rotation to refine material passing therebetween, an axially adjustable drive shaft passing through said housing, one of said plates being mounted on said drive shaft for rotation therewith, the other of said plates being fixed to said housing, means for introducing material to be refined into said housing between said plates, means for discharging refined material from said housing, means for pressurizing said housing with steam during the refining operation, said shaft being journaled within a quill disposed exteriorly of said housing, means on said base for supporting said quill to permit axial movement thereof with said shaft, means for rotating said shaft, means on said base providing selective axial positioning of said quill and said shaft and plate carried thereby, a seal assembly for sealing said shaft at its passage through said housing, said seal assembly comprising a quill extension extending axially from said quill and circumferentially overlying said shaft intermediate said shaft and said housing, means for sealing said quill extension for sliding axial movement with respect to said housing, a mechanical seal mounted between said quill extension and said shaft and adapted to move axially with said quill extension and shaft, a pressurized liquid cooling system for said mechanical seal, said cooling system pressure exceeding the pressure within said housing, and means for bleeding said cooling system liquid into said housing adjacent said mechanical seal to prevent particulate matter from reaching said mechanical seal.
 10. The invention as claimed in claim 9 wherein said means for sealing said quill extension for sliding axial movement with respect to said housing comprises a packing gland assembly.
 11. The invention as claimed in claim 9 including a labyrinth seal cooperatively mounted between said quill extension and said shaft and axially disposed between said housing interior and said mechanical seal, said cooling system liquid being bled into a region between said labyrinth seal and said mechanical seal to provide a purging flow of liquid through sAid labyrinth seal into said housing, thereby preventing the passage of particulate material into said mechanical seal.
 12. The invention as claimed in claim 9, wherein said mechanical seal comprises a pair of axially juxtaposed seal elements defining radially disposed parallel sealing surfaces, a non-rotating one of said seal elements being connected with said quill extension, a rotating one of said seal elements being connected to said shaft for rotation therewith, and means for resiliently biasing said seal elements together to provide a sealing engagement of said sealing surfaces.
 13. The invention as claimed in claim 9, wherein said cooling system liquid comprises water. 